Gun sighting system



April 15, 1969 A. R. NOLLET GUN SIGHTING SYSTEM Sheet of 4 Filed June 28, 1967 INVENTOR.

ANTHONY R. NOLLET ATTORNEYS Filed June 28, 1967 Sheet of4 INVENTOR. ANTHONY R. NOLLET ATTORNEYS April 15, 1969 A. R. NOLLET GUN SIGHTING SYSTEM Sheet Filed June 28. 1967 INVENTOR.

ANTHONY R. NOLLET ATTORNEYS 15, R NOLLET GUN SIGHTING SYSTEM Filed June 28. 1967 Sheet 4 of 4 FIG. 8

I nos-fl I INVENTOR. ANTHONY R. NOLLET ATTORNEYS United States Patent Office 3,438,305 Patented Apr. 15, 1969 Int. Cl. F4lg /14 US. C]. 89-41 14 Claims ABSTRACT OF THE DISCLOSURE The invention provides a gun sight for a machine gun mounted on a movable carrier, in which the sighting system automatically computes the velocity jump angle for the gun. There are several embodiments, in a first group of which a tiltable mounting frame is provided on which the gun may be rotated to sight on the target, and means are provided which tilt with the frame to adjust the gun sight to compensate for the velocity of the moving platform with respect to the target. In another embodiment, the machine gun is gimbaled on a rotatable base and forms the base of a parallelogram. A dummy gun constitutes the top of the parallelogram, and the forward end thereof is linked to the forward end of the gun, dummy gun and real gun thus being always parallel. The dummy gun may be swiveled and depressed to aim it and the real gun, the plane of the parallelogram swinging as this is done. A transverse arm in each embodiment supports a movable rear sight, the distance of this rear sight from the point at which the vertical axis of rotation of the gun barrel intersects the arm being adjustable so as to be set in proportion to the velocity of the gun carrier. Thus the velocity jump angle is computed when rear sight and fore sight are aligned.

This application is a continuation-in-part application of United States Patent Application Serial No. 593,875, filed November 14, 1966 now abandoned for Gun Sighting System."

Background of invention This invention relates to gun sights, and particularly to gun sights which are used either on a platform such as a helicopter or armored vehicle moving with respect to the target.

In order to hit a target from a moving platform, such as aircraft or armored vehicles, the gun must be aimed away from the line of sight to the target through an angle known as the lead angle. This lead angle is made up of the following components, which are listed in the order of their importance for flexible air-to-ground gunnery: (l) velocity jump; (2) gravity drop; (3) magnus effects (due to right-hand bullet spin); (4) allowance for target motion; and (5) coriolis effects (due to earths rotation). Of these effects, the velocity jump is by far the largest component. The magnus effects and con'olis effects are important in long range gunnery, but their importance in the relatively short range gunnery used from flying vehicles such as aircraft and helicopters is so small as compared to the major effect of train and elevation corrections, that they will not be considered in this invention.

Previous fire control systems designed to fire guns at a variety of angles from a moving platform have usually been gimbaled in a fashion known as train primary. elevation secondary. The train plane coincides with the *floor" of the vehicle on which the gun is mounted, and the elevation plane is normal thereto. The proper angle of orientation of the gun to hit the target is produced by two rotations, one being a rotation in the train plane and the other being a rotation in the elevation plane. The spherical trigonometry equations required to define these rotations are very complicated, and perhaps most undesirable, the expression for the component of the jump angle in the train plane is dependent on the component of the same jump angle in the elevation plane, and conversely. The computation of these angles requires a sophi-sticated computer, and to date such computers are used on naval vessels but not on aircraft. The present invention eliminates the necessity of computing the train and elevation components of the jump angle by performing the computation in the plane in which the problem occurs as will be shown later.

It is also very desirable to be able to detach a gun from its mounting on a helicopter quickly and simply, so that the gun may be used for perimeter guard duty, as an example. Concomitantly, the gun should be replaceable in its mounting quickly and simply, recapturing, as it is replaced, the accuracy and calibration of its moving platform sighting system.

Summary The invention broadly encompasses a simple, inexpensive, sighting means for guns of the aforesaid type, in which the sight automatically points the gun in the correct direction to correct for the velocity jump which is the major exterior ballistic effect for air-to-ground gunnery. The sighting system of this invention automatically computes the velocity jump for the above classes of guns. By constraining the gun so that its barrel always lies in a plane parallel with, or the same as, the plane defined by the platform velocity vector and the muzzle velocity vector, the velocity jump problem is solved by a simple mechanical system.

The invention also provides a gun sight system of the aforesaid class from which the gun may quickly and simply be detached and used with its regular sights, if the need arises, without harming the gun sight itself; and back into which the gun may be easily mounted for use on the moving platform.

Therefore, among the several objects and advantages of the invention may be noted the following:

One object of the invention is to provide a gun sighting system for guns on a platform moving in relationship to a target, which uses a simple, mechanical computing system to obtain the correct jump angle.

Another object of the invention is the provision of a sighting system of the above class in which the computation of the necessary jump angle is forced to lie in the plane in which the computation problem occurs.

A still further object of the invention is the provision of a sighting system of the above classes in which the sighting system is so designed that the gun itself may be quickly and expeditiously dismounted from the sighting mechanism for use away from the aircraft, and yet be equally easily remounted in such manner as to be accurately under the control of its sighting system.

Yet another object of the invention is the provision of a sighting system for guns on air vehicles having means by which the velocity vector of the moving vehicle with respect to earth, or its air speed, may be easily set in the positioning of the rear sight of the sighting system, either manually or automatically.

Another object of the invention is the provision of a sighting system for guns on moving vehicles in which a dummy gun is used for sighting, the dummy gun being gimbaled roll primary, train secondary, and being linked mechanically to the actual machine gun in such manner that although the machine gun is gimbaled train primary, elevation secondary, the barrels of the dummy gun and the machine gun remain parallel at all positions within the sighting capacity of the system.

Other objects will be in part apparent and in part obvious in the following description.

In the drawings in which are illustrated five embodiments of the invention:

FIG. 1 is an illustration of a first embodiment of the invention;

FIG. 2 is an illustration of a portion of a second embodiment of the invention, somewhat similar to the first embodiment, the drawing omitting for the purpose of clarity certain elements common to both embodiments and shown in FIG. 1;

FIG. 3 is an illustration of a portion of a third embodiment of the invention, omitting for the sake of clarity certain elements common to all the embodiments and shown in FIG. 1;

FIG. 4 is an illustration of a portion of a fourth embodiment, again omitting elements common to all embodiments and shown in FIG. 1;

FIG. 5 is a vector analysis relating the vector velocity of the forward motion of the vehicle, the vector muzzle velocity of the bullet leaving the gun, and the line of sight;

FIG. 6 is an illustration showing on three dimensional axes the problem involved in computing the proper jump angle from the train and elevation angular relationships;

FIG. 7 is an illustration showing a vector analysis applicable to the sighting system of this invention and directly related to the vector analysis of FIG. 5;

FIG. 8 is an illustration of a fifth embodiment of the invention in which a dummy gun is used for sighting; and

FIG. 9 is a line drawing showing the interrelation of the dummy gun sighting line and the machine gun firing line.

Throughout the drawings, similar reference characters indicate corresponding parts, and dimensions of certain of the elements of the invention may have modified and/or exaggerated for the purposes of clarity of illustration.

It has been mentioned previously that the problem of computing the proper jump angle is rather complicated, and in presently known systems has required rather sophisticated computers for such computation and proper setting of the direction of the barrel of the gun in reference to the target, if a hit is to be made. Referring first to FIG. 5, there is given a vector analysis which is well known in the art but is presented here in order to clarify the discussion below showing the difficulty of computing the proper jump angle. In the diagram V is the velocity vector of the moving platform (a helicopter, for example) with respect to earth. V is the muzzle velocity vector of the gun. Neglecting curvature effects which are small compared with velocity jump, the bullet from the gun travels on a course given by the sum of the muzzle velocity vector and the helicopter velocity vector, that is, T -l-V The angle between the muzzle velocity vector T and the sum of the muzzle velocity vector and the helicopter velocity vector (V +V is designated as a, the velocity jump angle. If this angle is computed correctly, and neglecting the exterior ballistic curvature effects, the bullet from the gun will hit the target, provided that the target is located in the direction given by the vector sum V +V The angle between the helicopter velocity vector 7 and the target is designated as the angle [8. Then:

The disadvantage of attempting to compute the velocity jump angle a in conventionally gimbaled sighting system may be shown in FIG. 6. In FIG. 6, Z is the axis of the helicopter rotor, the X-axis is the direction of flight of the helicopter, and the Y-axis is transverse to the axis of flight, and thus can represent, for example, a wing of 7 sin a=V sin B and a=arc sin sin [3 the helicopter. In this drawing, 7 again is the muzzle velocity vector, V is the vehicle velocity vector, and the line of sight to the target is the vector sum V +V The angle a is the jump angle, and the angle 5 is the angle between the direction of fiight of the helicopter and the line of sight, that is, the target.

The angles a and 13 are each produced by two rotationsa rotation in the train plane and a rotation in the elevation plane. The spherical trigonometry equations required to define the train and elevation rotations are very complicated. Perhaps most undesirably, the expression for the component of a in the train plane is dependent on the component of a in the elevation plane, and conversely. Thus it is not believed that any turret systems, save, possibly those used on Navy vessels, have ever computed the train and elevation components of the angle a. perfectly. Furthermore, the analog or digital computers which computed these train and elevation components of the angle at approximately were, and are, sophisticated computers.

In typical existing fire control systems, the angles 0 and p are measured by two speed syncros and fed to a computer. In the computer, they are combined with other variables and the computed gun angles 6' and are transmitted to the gun turret as train and elevation gun orders respectively. As noted previously, the equations required to compute 6' and are complicated spherical trigonometric equations.

This invention eliminates the necessity of computing the train and elevation components of the angle a by performing the computation in the plane in which the problem occurs as also shown in FIG. 6. This plane is the plane determined by the vectors and V and the vector sum RH-T Consider, for purposes of illustration, that the plane containing V and V were, in fact, a metal plate hinged about the X-axis. It now, the axis of the gun barrel is constrained to lie along the T vector, and the aforesaid plate is hinged to move up and down (as drawn) about the X-axis, with the gun enabled to rotate in the aforesaid plate about the intersection of the three axes, then the computation of the jump angle a will be computed in the aforesaid plate (ie, in the plane determined by T and V Referring now to FIG. 7, a schematic analysis of the gun mounting and sight system of this invention is given. In this illustration, the X-axis represents the flight of the helicopter, point is the axis of rotation of the gun barrel, point 92 is the rear sight, and the line r joining points 90 and 92 lies on the X-axis. Line R represents the gun barrel, and point 94 represents the front sight of the gun. The angle a is that defined by the line R and the line between the rear and front sights. Let line d be perpendicular from point 90 to the line of sight. Then:

d=R sin a=r sin 13 The similarity between this equation and that given earlier herein is apparent. If, now, R is made proportional to V and r is made proportional to then the mounting and sighting system sketched in FIG. 7 will exactly compute the correct jump angle a.

Referring now to FIG. 1, there is shown a first embodiment of the invention comprisng a gun mount and sighting system for operating in the FIG. 7 manner. A support or base 2 is provided which is fastened to the helicopter or other moving vehicle, base 2 continuing as an extension 4 rotatable thereon for the purpose of providing an adjustment for the crab angle of the helicopter. At the top of the extension 4 is provided a U-shaped yoke comprising the opposed upwardly extending arms 6 attached to a base or bight 8, the bight 8 being attached fixedly to the top of 4 so that there is no gimbaling action. This attachment may be made by conventional means and will not further be described herein. A second support or cradle 9 is shown, comprising the opposed upwardly extending arms and 12 and a base or bight 14. A pair of pivots 16 are attached to the upper ends of the arms 6, and tiltably attached to the pivots 16 are the arms 10 and 12 so that cradle 9 may tilt on the pivots. The axis defined by pivots 16 will be hereinafter called (as respects FIGS. 17) the tilt axis, and this axis is so adjusted on the helicopter that it is in the direction of flight of the helicopter. This tilt axis is indicated by numeral 18.

Attached to the bight 14 is a stationary platform 20, the platform 20 being attached by conventional means such as welding to the bight. Rotatably mounted on platform 20 is gun mounting platform 22 about a central pivot point 21, this rotating attachment being conventional in nature. The axis of rotation of platform 22 on platform 20 will hereinafter be called the axis of rotation (of the gun).

Attached to the platform 22 as an illustration of a method of attaching a gun thereto are the upright supports 24, and a gun illustrated generally by numeral 26 is mounted on the uprights 24 by conventional but detachable mounts, so that the gun 26 may be removed from the platform 22. The method of so mounting the gun on the upright 24 is not detailed, since it is conventional, but can be done, for example, by conventional snappins 28, or by means of an axle extending through the gun and through the upper portions of the mounts 24, this pin being removably held in position by some kind of quick-detach locking arrangement which may be easily removed or replaced by the gunner. The details of how the gun is removably held on platform 22 are not a part of this invention, except for the fact that the gun is so removably held.

Also mounted on platform 22 are brackets 30 which are shown as one means of being sure that the gun does not rotate about the axle 28. Supports 30 are not necessary for the invention since the gun can be flush-mounted on the platform 22 so that it does not rock thereon. However, if minor initial corrections are necessary in aligning the sights properly, then by means of the brackets 30 and the adjusting screws 32, such minor corrections may be made. However, it is to be carefully noted that the gun in use does not tilt with respect to the platform 22, although the gun and its platform 22 can rotate about the aforesaid axis of rotation 21 on the bight 14. Furthermore, the gun and cradle 9 tilt as a unit about the axis of tilt defined by the pivots 16.

The gun 26 may be a conventional one such as commonly used on helicopters, and comprises the breach assembly 34 and a barrel 36. At the forward end of barrel 36 is mounted the front sight of the gun which, in this embodiment, is swiveled on the barrel. Swiveling may be done by any number of means, and as an example, there is shown a small platform 38 fixed to the gun barrel, and pivoted thereon is a front sight supporting platform 40, the pivoting being done by a conventional means. A V-shaped front sight 42 is anchored to the platform 40. (Although not part of this invention, typical pedestals or legs 44 are afiixed rotatably to the forward portion of the gun so that the gun, when used on the ground, may be supported.)

Joining the upper ends of the arms 10 and 12 is a rear-sight supporting bar 46 which may, for example, be a steel rod having its ends conventionally fastened to the arms 10 and 12 as shown. With the construction shown, the supporting bar 46 is always aligned in the direction of the axis of flight 18. This alignment exists regardless of the angle of tilt of the cradle 9 and the gun 26 about the pivots 16.

Slidably arranged on the rear sight support bar 46 is a mounting plate 48 which may be fixed in an adjusted position on the bar 46 by means of, for example, a set screw 50. Rotatably mounted by conventional means on the base 48 is a rear sight base or platform 52, and mounted on the latter is a ring-type rear sight 54. A link, in this instance a rod 56, is connected to the platform 40, as by the clevis and pin connection 58 as shown, the rod 56 passing slidably through the rear sight base 52 by means of a suitably provided hole therein.

With the above construction, it will be observed that the necessary relationships set forth in the above discussion regarding the helicopter velocity vector, the muzzle velocity vector, the line of sight, and the jump angle at are automatically provided regardless of how the gun 26 is rotated on its axis of rotation, and regardless of how the gun is tilted on the axis of tilt 18. The platform (helicopter) velocity vector V is established, in accordance with the actual velocity of the helicopter with respect to ground, by the adjustment of the base 48 along the rearsight support-bar 46, measured from the intersection of the said axis of rotation and the sight bar, this adjustment being made by the gunner manually in this embodiment. The gun 26 is so mounted on the platform 22 that the distance along the muzzle of the gun from the front sight 42 to the aforesaid axis of rotation 21 is proportional to the muzzle velocity of the bullet as it leaves the gun, this distance therefore representing the muzzle velocity vector T With this construction, the rod 56 then is parallel to the sight line, the jump angle a being the angle included between the sight line from the center of the rear sight 54 and the front sight 42, and a line parallel to the axis of the barrel and extending from the front sight back to the dotted line 66 which is a projection of the said axis of rotation 21.

It has been pointed out above that the rear sight 54 is a ring sight, and as an example may have the rings 60, 62, and 64. Each of these rings is so proportioned as to account for the gravitational drop in the bullet for a given distance. With the construction shown in this embodiment, as the gun 26 is rotated about its said axis of rotation 21 on the base 20, an additional effect of the rod 56 is always to maintain the plane of the ring sight 54 perpendicular to the direction of rod 56 and thus to the sight line. Also, the rotation of the gun about axis 21 causes the platform 40 to rotate on the supporting platform 38 in such manner that the V-sight 42 is always aligned with the rod 56. By this construction, greater accuracy is obtained in allowing for gravity drop of the bullet.

Referring now to FIG. 2, there is shown a second embodiment of this invention having to do with the arrangement and construction of the front and rear sight elements. The remaining features of the embodiment are the same as in the FIG. 1 embodiment, and are omitted from this figure for purposes of clarity. Again, as in the FIG. 1 embodiment, the arms 10 and 12 of the cradle 9 are shown, these arms being pivoted (exactly as in the FIG. 1 embodiment) about pivots 16 shown in FIG. 1. A rear sight bar 46 is provided as in the FIG. 1 embodiment. The gun is the same as in the FIG. 1 embodiment, and has the gun barrel 36, the gun being rotatably on axis of rotation 21.

In this embodiment, however, the sights are simplified as follows: Adjustably mounted on the bar 46 in order to get the rear sight according to the vector V is the rear sight mounting plate 70. In this instance, the rear sight bar 46 is again shown as a rod, and the base 70 is a simple base having a transverse hole slidable on the bar 46, and having a set screw 72 for locking the base 70 in its position along the bar 46. The rear sight 74 in this embodiment is a bead sight.

On the forward end of the gun barrel is fixedly mounted by conventional means such as a platform 76 a ring sight 78 having the rings 80-, 82, and 84. While in this embodiment, the ring sight 78 is shown as being fixedly mounted to the gun barrel, nevertheless, if desired, the platform 76 may be made rotatable as in the FIG. 1 embodiment, with a corresponding bar 56 and a rotatable base mount for the rear sight 74. However, when it is realized that the actual excursion of the angle a: from the position that the rod 56 would overlie the gun barrel to the furthermost movement of the rear sight base (in order to adjust for the velocity vector V produces relatively little rotation of the front sight, it will be found that even though the otherwise circular appearing forsight in the FIG. 2 embodiment appears slightly oval in shape at the maximum excursion of the base 70 away from the aforesaid axis of rotation, this change in shape to that of an oval is not enough seriously to interfere with sighting accuracy.

As in the first embodiment, the jump angle a is the angle included between the sight line (i.e., bead rearsight to center of front sight) and the line from the center of the front sight parallel to the axis of the gun barrel. As the gunner moves the gun about the axis of rotation to maintain the target in the sight line, the jump angle is automatically computed regardless of the tilt of the gun and the rear sight about the said axis of tilt.

Referring now to FIG. 3, there is shown a third embodiment, which is the same as the FIG. 1 embodiment except for the elimination of an actual front sight and the substitution of an intensifier rear sight for the ring sight of the first embodiment. The intensifier rear sight, drawn schematically, may be one of several varieties known to the art, and in its simplest form is shown as a large objective lens telescope 90 fixedly mounted on the rear sight platform 5-2 which in turn is rotatably mounted on the platform or base 48, the latter being slidable on the rear sight support bar 46 as in the FIG. 1 embodiment. The linkage rod 56 slides in the base 52 and has its forward end pivoted to the forward end of the gun barrel. The gun is rotatable about axis of rotation 21. Again, as in the FIG. 1 embodiment, the jump angle a is the angle included between the sight line (in this embodiment the optical axis of the sight) and a line parallel to the barrel of the gun and extending from the point where the optical axis of the rear sight intersects the upward projection of the axis of pivoting of the rod 56 on the forward end of the barrel, backwardly to the point of intersection of said line with the upward projection of the axis of rotation 21 of the gun. The distance from the pivot point of rod 56 to the gun barrel to said point of intersection represents the vector 7 and the distance of the mounting point of sight 90 on platform 52 from said point of intersection represents the vector V Referring now to FIG. 4 for a fourth embodiment of the invention, this embodiment is the same as the FIG. 1 embodiment except for the substitution of automatic means for setting the velocity vector V for the manual means of the FIG. 1 embodiment (and also for the FIGS. 2 and 3 embodiments). In this embodiment (from which have been omitted details common to the FIG. 1 embodiment) the cradle arms 10 and 12 are provided, between the upper ends of which extends a lead-screw 94. Screw 94 is mounted in suitable hearings in arms 10 and 12, and is rotated by motor 96 mounted on arm 10. Screw 94 is threaded into a suitably threaded hole in a rear sight base 92, so that rotation of screw 94 will traverse base 92 back and forth along the screw. The ring sight 54 of the FIG. 1 embodiment is mounted on the table 52 which is rotatably mounted on base 92. Rod 56 couples table 52 to the front sight of the gun, as in FIG. 1. The leads 98 from motor 96 are suitably connected to a device (such as a Doppler velocity computer) which measures the effective velocity of the helicopter with respect to ground, and transforms this measurement into rotation of screw 94 to adjust the position of base 92 automatically to be proportional to the ground speed. The details of the ground speed measuring device are not part of this invention, and consequently will not be recited herein, since they are well-known.

It will be observed that in all these embodiments, once the vector V has been established along the respective sight bars 46 and .134, this vector does not change with movement of the gun.

It will also be noted that in all embodiments, the gun itself may be quickly dismounted from its cradle without damage thereto or upsetting its calibration. Similarly, the gun may be quickly remounted in its sighting cradle, and all that is necessary to adjust is the traverse of the rearsight base to set to reflect the proper V vector.

Referring now to FIGS. 8 and 9, there is shown a fifth embodiment of the invention utilizing the above principles, but which is in some instances more readily adaptable to existing machine gun mountings than are the above embodiments, since the ordinary machine gun gimbaling of train primary, elevation secondary is not changed. However, in this fifth embodiment, a dummy gun sight is provided which, like the above embodiments, is gimbaled roll primary, train secondary, and the machine gun and dummy sight gun are linked together mechanically so that the machine gun always follows in parallel relationship the movement of the dummy sighting gun, the parallel linking relationship being essentially a parallelogram with pivoted arms. Thus, since the machine gun itself is constrained to follow the sighting gun, and since the computation of the jump angle occurs in the dummy gun sighting system of this fifth embodiment just as it does in the above embodiments, the machine gun itself will be so sighted.

Referring now to FIG. 8, a somewhat schematic illus tration of a machine gun and the sighting mechanism of this embodiment is shown, actual details of machine gun construction being omitted since they are not a part of this invention. A U-shapecl frame 102 is rotatably mounted by a conventional bearing 104 on a pedestal 106, for example, which is fastened to the floor of the carrier (a helicopter, for example). By means of the bearing 104, it is possible to rotate the frame gun about the axis of the pedestal 106 and lock it thereon in a direction parallel to the carrier flight direction.

A machine gun 108 is tiltably mounted in a yoke 110 which is rotatably mounted in a bearing 112, the latter being fastened to the frame 102. Thus, the machine gun is gimbaled train primary, elevation secondary. Spanning the upper ends of the arms 116 and 118 of frame 102 is the sight support bar 114 (the latter also being called herein a velocity vector bar), the bar extending horizontally over bearing 112 so as to be intersected by the axis thereof. The ends of bar 114 are mounted rotatably in the ends of the arms 116 and 118 by conventional means, and the bar is provided with a flat top 120. Slidable upon the sighting bar 114 is a sleeve 122 which may be locked in position on the sighting bar by a set-screw 123. A connecting rod (or sight-line" rod) 124 has one end fixed to a hub 126 rotatably mounted on sleeve 118. Mounted on hub 126 is a ring sight 128 similar to ring sight 54.

Pivotally secured to the bar 114 at a point determined by the intersection of the axis of the bearing 112 therewith is an elongated member 130 which hereinafter is called a dummy gun." The rear (as viewed) end of the dummy gun is pivoted by a yoke 13-2 to the bar 1 14, so that it may swing in a plane determined by the axis of the support bar 114 and the axis of the dummy gun itself. The dummy gun may be tilted in elevation because of rotatability of the sight bar 114 in the arms 116 and 118. It will be noted that as the dummy gun is tilted, the sight 128 also tilts. The distance from sleeve 134 to the sight support bar 114 along the gun 108 is made proportional to the muzzle velocity of the gun.

Afiixed to the dummy gun is a T-sleeve 134 to which is rotatably fastened another T-sleeve 136. The sight-line rod 124 is slidably restrained within the bore of sleeve 136. Thus, the bar 124, dummy gun .130 and support bar, together with their respective pivoting or gimbaling means, constitute a roll primary, train secondary, gimbal system in which the jump angle is automatically computed re gardless of the position of dummy gun 130.

Attached to the barrel of the machine gun 108 and to the end of rod 130 is an H-shaped connecting link 140, the lower legs thereof being pivoted to the machine barrel by pivots 142. The upper legs are pivoted to a sleeve 144 by means of pivots 146. Sleeve 144 is rotatably fastened to the barrel of gun 108 by means of conventional collars 148 aflixed to the barrel by set screws. The distance of the axial line of pivots 146 from the axial line of pivots 142 is equal to the distance from the axis of bar 114 to the pivots holding the gun 108 to the yoke 110. Thus, a parallelogram is formed with top being dummy gun 130, base being gun 108, one side being link 140, and the other side being the imaginary line from the bar 5114 to the gun 108.

With this construction it will be seen that the dummy gun is gimbaled roll primary, train secondary, while the machine gun itself is gimbaled train primary, elevation secondary. However, the gun 108 is constrained to be parallel at all times to the dummy gun 130. As a result, the actual aiming of gun 108 will be in accord with the aim of dummy gun 130, with the result that gun 108 will be aimed as if it were, in effect, gimbaled roll primary, train secondary. There are several advantages of this fifth embodiment as compared to the first four embodiments. The first of these is that as the gun 108 is traversed and elevated, it cannot turn about its own axis, whereas in the first four embodiments, the gun itself turns about its own axis as it is moved in train and depressed in elevation.

Another advantage of the fifth embodiment is that the sighting system itself may be mounted separately on the frame of the aircraft, instead of being a unit part of the mounting for the machine gun, with resultant lessening of transfer of vibration from the machine gun to the sight. Furthermore, recoil of the gun during firing will not be transmitted to the gun sight, itself, due to the pivotal linkages between the arms of the parallelogram.

Referring to FIG. 9 which is a line drawing illustrating the principles of the fifth embodiment, line aa' corresponds to the dummy gun 130, line a'b' corresponds to the link 140, line bb' corresponds to the length along the gun barrel from the link 140 to the pivots 111 in yoke 110, and the line ab is the line representing the distance between the two latter points. Actually, as indicated on FIG. 9, line ab is a reference line which is parallel to the aircraft Z axis, that is, parallel to the rotor of a helicopter, for example. The line cd represents the sighting rod 124, and thus the angle between ad and cd is the jump angle. The distance r shown on FIG. 9 (that is, the line ac) is the distance that the rear sight 128 is from the axis of the gun 108, and may be set to compensate for the ground speed of the aircraft. The line eb is a reference line parallel with the aircraft roll axis. The aforementioned parallelogram comprises the lines aa, a'b', b'b and ab.

In view of the above it will be seen that the several objects of the invention are achieved and other advantageous results attained.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

Having described the invention, what is claimed is:

1. In combination, a gun and a sighting means therefor for use on a vehicle moving with respect to a target, the sighting system comprising a triangle gimbaled roll primary, train secondary, about the base of the triangle, the combination comprising a first base rotatably mounted on the vehicle about a first axis; a rear sight supporting bar mounted on said base and adapted by rotation of the first base to be aligned with the direction of the vehicle, at least a portion of the bar constituting the base of said triangle; a second base rotatably mounted on the first base about a second axis intersecting said sight bar at a point; a gun mounted on the second base and rotatable about said second axis, and also being adapted to be pivoted with respect to said first base to change the gun's elevation; the axis of the barrel of the gun lying in a plane containing a first line constituting one leg of said triangle and extending from said point; a rear sight member mounted on said rear sight support bar and being movable to a position on said bar at which the distance of the sight from said point is proportional to the speed of the vehicle, said distance being equal to said base of the triangle; the other leg of said triangle constituting a second line extending from said rear sight to a location on said one leg removed from said point a distance proportional to the muzzle velocity of a bullet fired from said gun; the jump angle of the gun comprising the angle between said first and second lines; and means operatively associated with the gun and movable therewith, whereby when the gun is moved, the plane of said triangle is also moved, said jump angle for a given position of the target being thereby computed in the plane of said triangle and applied to the direction of pointing of the gun.

2. In combination, a gun and a sighting system therefor for use on a vehicle moving with respect to a target, comprising a base rotatably mounted on the vehicle and having a transverse first axis alignable with the direction of motion of the vehicle; a gun mounted on said base and rotatable thereon on a second axis, the latter being vertically perpendicular to said first axis; a sight supporting bar mounted on the base and aligned with the first axis and positioned to be intersected by said second axis; a rear sight member movable along said bar with respect to a point defined by the intersection of said bar and said second axis, the distance between said sight and said point of intersection being settable to be proportional to the ground speed of the vehicle; and sighting means attached to the forward portion of the gun whereby a line of sight may be obtained between said rear sight and said sighting means, the angle between said line of sight and the gun barrel constituting approximately the jump angle, and the distance from said point of intersection to said sighting means being proportional to the muzzle velocity of the gun.

3. In combination, a gun and sighting system therefor for use on a vehicle moving with respect to a target, comprising a first base on the vehicle; a second base tiltably mounted on the first base about an axis of tilt, the latter being adjustably alignable with the direction of motion of the vehicle; a gun rotatably mounted on the second base on an axis of rotation tilting with the latter about the axis of tilt; a rear sight support bar mounted on the second base and lying parallel with said axis of tilt in such position as to be intersected by said axis of rotation at a point of intersection; and a rear sight member movable along said support bar toward and away from said point; the gun having a reference sighting point at its muzzle end, with the distance from said sighting point to said point of intersection being proportional to the muzzle velocity of the guns bullet and the distance of the rear sight from said point of intersection being settable to be proportional to the speed of the vehicle with respect to ground in the direction of said axis of tilt.

4. The combination of claim 3 including a link member connecting said reference sighting point and said rear sight member and including rotatable means mounting 11 said rear sight member to said support bar, said link member sliding in the rotatable means and turning the latter as the gun is rotated on said axis of rotation.

5. The combination of claim 3 in which the rear sight is a post-and-bead sight, and including a front sight mounted at said reference sighting point, the front sight being a calibrated ring sight.

6. The combination of claim 3 in which the rear sight support bar is a lead screw rotatably supported in bearings in the second support and threadably engaging the rear sight member for traversal thereof as the screw turns.

7. The combination of claim 3 in which the rear sight support bar is a lead screw rotatable in bearings in said second support and threadably engaging the rear sight member so as to adjust the position of the latter by rotating, said combination including a motor operatively connected to the lead screw for turning the latter to position the rear sight member, the motor being adapted to be energized by means having an electrical output responsive to the velocity of the vehicle in respect to ground in the direction of the axis of tilt.

8. The combination of claim 3 including means coupling the gun and rear sight member for turning the latter as the gun is rotated about said axis of rotation, whereby the line of sight through the rear sight member always passes through said reference sighting point as the gun is so rotated.

9. The combination of claim 3 in which the first base includes a pair of spaced-apart arms forming a yoke, the arms lying in opposed relationship in a plane parallel to the said direction of motion; the second base includes a U-shaped cradle having a pair of opposed arms and a bight, the latter arms being pivotally connected to the arms of the first base by pivots lying on said axis of tilt; gun mounting means for rotatably mounting the gun on said bight to rotate on said axis of rotation; quick detach means for mounting the gun on said gun mounting means; and the rear sight support bar extends across the upper ends of the arms of said cradle.

10. In combination, a gun and sighting system there for for use on a vehicle moving with respect to a target, comprising a base rotatable with respect to the vehicle in train primary, a gun mounted on said base on pivots, the gun being rotatable in elevation secondary; an elongated rear sight support bar adjustably mounted on the vehicle so as to be alignable with the direction of motion of the vehicle and overlying said base so that the axis of rotation thereof intersects said support bar at a point above the gun; an elongated direction member pivoted at one end to said support bar at said point and rotatable in a plane containing both the support bar and said direction member; a rear sight movably attached to said support bar and positionable thereon so that the distance from the sight to said point is proportional to the ground speed of the vehicle; a connecting link pivotally connecting the forward part of the gun to the other end of said direction member whereby the gun barrel is held parallel to said direction member regardless of the tilt of the latter in elevation; connecting means fastened to the forward portion of said direction member at a position distant from said point an amount proportional to the muzzle velocity of the gun; and first means slidably connecting said connecting means with the rear sight, whereby said support bar, said direction member and said first means comprise a tiltable sighting plane for governing the position of the gun and in which the jump angle of the guns direction is computed mechanically.

11. A sighting system for a gun mounted on a carrier movable with respect to a target, comprising elongated rear-sight supporting means, said means being adapted to be aligned with the direction of motion of the carrier; at rear sight movably mounted on said supporting means and positionable thereon at a distance removed from a point thereon proportional to the speed of the vehicle; and front sighting means tiltably mounted on the carrier on a line extending from said point and alignable with the rear sight; the line between the front sighting means and the rear sight constituting the first leg of a triangle; the line between the front sight and said point constituting the second leg of said triangle, the length of said second leg being proportional to the muzzle velocity of bullets fired from said gun; and the line along said supporting means from said rear sight to said point constituting the base of said triangle; said triangle being rotatable about the axis of the supporting means; and the front sighting means being movable in an are about said point as a center to align said first side of the triangle with said target.

12. The sighting system of claim 11 in which said front sighting means constitutes the from sight of said gun.

13. The sighting system of claim 11 including a dummy gun, the dummy gun being pivoted by the rear end to said supporting means at said point, and the axis of said dummy gun coinciding with said first leg of the triangle, with the front sighting means mounted on the forward end of the dummy gun.

14. The sighting system of claim 11 in which the rear sight supporting means is rotatable about its longitudinal axis, said rear-axis rotating therewith, and including a dummy gun pivoted by a rear end to said supporting means and rotatable about said axis therewith, the axis of said dummy gun coinciding with the first leg of the triangle, and the front sighting means being mounted on the forward end of the dummy gun.

References Cited UNITED STATES PATENTS 1,650,628 11/1927 Inglis 3349 2,363,523 11/1944 Greenblatt et al. 3349 2,534,225 12/1950 Brown 33-49 2,642,662 6/1953 Lyon 89-4l 2,870,678 l/l959 Girouard et a1. 89l.8l5 X SAMUEL W. ENGLE, Primary Examiner.

US. Cl. X.R. 33-49 

